The present teachings relates to detection of concealed objects.
The detection of weapons, contraband, and other concealed objects is of significant interest at security checkpoints and the like. Explosives detection for aviation security has been an area of federal concern for many years.
Much effort has been focused on direct detection of explosive materials in carry-on and checked luggage, but techniques have also been developed to detect and identify residual traces that may indicate a passenger's recent contact with explosive materials. The trace detection techniques use separation and detection technologies, such as mass spectrometry, gas chromatography, chemical luminescence, or ion mobility spectrometry, to measure the chemical properties of vapor or particulate matter collected from passengers or their carry-on luggage. Parallel efforts in explosives vapor detection have employed specially trained animals, usually dogs, as detectors.
The effectiveness of chemical trace analysis is highly dependent on three distinct steps: (1) sample collection, (2) sample analysis, and (3) comparison of results with known standards. If any of these steps is suboptimal, the test may fail to detect explosives that are present. When trace analysis is used for passenger screening, additional goals may include nonintrusive or minimally intrusive sample collection, fast sample analysis and identification, and low cost. While no universal solution has yet been achieved, ion mobility spectrometry is most often used in currently deployed equipment.
Several technologies have been developed and deployed on a test or prototype basis. One approach is to direct passengers through a portal, similar to a large doorframe, that contains detectors able to collect, analyze, and identify explosive residues on the person's body or clothing. The portal may rely on the passenger's own body heat to volatilize traces of explosive material for detection as a vapor, or it may use puffs of air that can dislodge small particles as an aerosol. Alternatively, a handheld vacuum “wand” may be used to collect a sample. In both cases, the collected samples are analyzed chemically.
A different approach is to test an object handled by the passenger, such as a boarding pass, for residues transferred from the passenger's hands. In this case, the secondary object is used as the carrier between the passenger and the analyzing equipment. The olfactory ability of dogs is sensitive enough to detect trace amounts of many compounds, but several factors have inhibited the regular use of canines as passenger explosives trace detectors. Dogs trained in explosives detection can generally only work for brief periods, have significant upkeep costs, are unable to communicate the identity of the detected explosives residue, and require a human handler when performing their detection role. In addition, direct contact between dogs and airline passengers raises liability concerns.
Metallic objects can be detected utilizing a magnetometer. Unfortunately, this approach does not detect most organic polymer and composite materials that may be used to fabricate firearms, explosives, and other objects which are frequently the subject of security inspections.
In another approach, millimeter wave electromagnetic radiation is applied to provide images that can reveal objects concealed by clothing. This approach typically depends on the ability of a human inspector to visually detect one or more suspect objects from the resulting image. Accordingly, there are intrinsic speed limitations in these approaches, and such approaches are subject to variation with the ability of different inspectors. Moreover, because these systems can provide detailed images of body parts that are ordinarily intended to be hidden by clothing, utilization of a human inspector can be embarrassing to the person being inspected, and may pose a concern that privacy rights are being violated. Thus, there is an on going demand for further contributions in this area of technology.
In conventional systems, infrared detection of concealed objects has failed in the most cases because infrared camera reacts only on heat differences between the object under cloth and background cloth. If an object is in contact with a body (for example, a human body) for long enough to come to approximate thermal equilibrium, this difference in some cases will be negligible and contrast of the concealed object (for example, under cloth) is not enough for detection.